An immunoassay is a biochemical test that measures the presence or concentration of a macromolecule or a small molecule in a solution, based on the ability of an antibody to recognize and bind a specific antigen, wherein a measurable signal is produced upon binding.
The molecule detected by the immunoassay is referred to as an “analyte” and is generally a protein.
Immunoassays may be used for detection of an analyte in a biological fluid e.g. blood or urine, or in a non-biological fluid e.g. drinking water.
Most immunoassays for detection of an analyte in a biological fluid must be employed by medical personnel, often requiring the use of additional equipment, such that testing must be carried out at medical facilities.
An example of an analyte which may be detected in a biological fluid is meconium. The colon of a fetus during gestation fills with meconium, the fetal feces comprising bile and its metabolites, gastrointestinal and pancreatic secretions, mucus, cellular debris, swallowed vernix caseosa, and blood. In a significant minority of births, the fetus ceases to be continent and excretes meconium into the amniotic fluid. It is important to be aware of such an occurrence for the future mother and for the obstetrics personnel.
The fetus may pass stool to the amniotic fluid in response to stress (e.g., hypoxemia) and then inhale it into the lungs. Fetal stool, meconium, is toxic in the lungs, it can obstruct airways, and also does harm by other mechanisms, resulting in meconium aspiration syndrome (MAS). Meconium aspiration may occur before, during, and after labor. About 13% of all live births are complicated by meconium-stained amniotic fluid (MSAF), and about 30,000 develop MAS annually in the United States, leading to the death of 1000 children. MSAF is associated with an increased risk for perinatal complications during labor and delivery (e.g., low Apgar score, higher risk for cesarean section, and higher admission rate to neonatal intensive care unit. MSAF is considered to be a marker for possible fetal compromise. Prenatal detection of meconium in the amniotic fluid can alert a caregiver or patient to intrauterine fetal distress and might have an important role in reducing the incidence and consequences of MAS, fetal hypoxemia, and cerebral palsy. Moreover, when meconium concentration is high—designated herein as thick meconium, the amniotic fluid has a dark green opaque color. Heavy (thick) MSAF may indicate worse fetal/neonatal prognosis than light (thin) MSAF.
There is a consensus that a pregnant woman with MSAF should be carefully evaluated for fetal well-being in order to reduce the chances of irreversible damage to the fetus/newborn. To date, a number of invasive and non-invasive methods and devices are known to identify MSAF. Amniocentesis is an invasive sampling procedure removing a small volume of the amniotic liquid for in vitro testing. U.S. Pat. No. 5,361,759 describes an invasive method for detection of undesired components, including meconium, in amniotic fluid by absorbance spectroscopy of a sample of amniotic fluid acquired by penetrating the amniotic sac. U.S. Pat. No. 5,713,351 describes an invasive method for the detection of meconium in amniotic fluid by penetrating the amniotic sac with a probe and withdrawing amniotic fluid through the lumen of the probe into an observation chamber. Amnioscopy is a less invasive technique, enabling direct observation of the forebag of an amniotic sac to look for meconium staining; it may help in detecting heavy staining by meconium, but milder cases remain undetected, and the method may require an undesirable degree of cervical dilation. U.S. Pat. No. 5,172,693 describes the detection of meconium in the amniotic sac by detecting fluorescence of the bilirubin component of meconium, placing a probe against the uterine wall and irradiating the amniotic fluid through the body tissues by excitation light, leading to characteristic fluorescence of eventual meconium components in vivo. US 2010/0324391 describes a device for detecting meconium in amniotic fluid by fluorescent measurement of zinc coproforphyrin in vivo. U.S. Pat. No. 6,044,284 relates to an apparatus for measuring the concentration of meconium in amniotic fluid by employing optical sensors measuring the fluid transmittance in vivo. The above approaches are characterized by physical or optical penetration into the amniotic sac. U.S. Pat. No. 5,514,598 describes a non-invasive method to detect MSAF: a specific meconium protein (14 kilodaltons) can be detected by immunological techniques.
All approaches described above must be employed by professional personnel and, therefore, limit their use to medical facilities. As a matter of fact, high quality fetal wellbeing monitoring is still restricted to skilled personnel (e.g., ultrasonographic fetal heart rate tracing, biophysical profiling, and amniotic fluid indexing).
Rupture of the amniotic sac membranes may occur throughout almost the whole pregnancy period. When rupture of membranes (ROM) occurs, umbilical cord (UC) prolapse (0.5 percent of all pregnancies) can be one of the biggest threats to the fetus. UC prolapse occurs when a UC loop precedes the leading part of the fetus (during spillage of amniotic fluid from the uterine cavity). During this process the UC loop may be compressed and result in imminent fetal asphyxia. In a significant minority of term pregnancies (37-40 gestational weeks) 10-15% of women arrive at the hospital with their ‘water already broken’. ROM and the associated severe complications (e.g., UC compression, placental abruption) may occur at home, away from a medical facility. Failure to recognize and immediately treat these complications may result in fetal death. A well-established possible indicator for these complications is MSAF.
To date, there is no simple accurate method or device that enables home detection of MSAF by lay people. Furthermore, nowadays MSAF can be detected at home by the naked eye only. However, in a significant number of events MSAF may be bloody or may be lightly stained and therefore not detectable by the naked eye. Another important aspect is the ability to identify the etiology for MSAF (and the possible fetal distress) at home by lay people, as well as the potential severity of the MSAF. To date, there is no simple method or device enabling such a thing. It is an object of this invention to enable the detection of MSAF by lay personnel.
Thus, there is a need for: a) Providing a method of detecting MSAF without penetration into the amniotic sac; b) Providing a sensitive and specific method and kit for detecting MSAF (including bloody or lightly stained MSAF) without employing complex analytical tools or devices; c) Providing a method and a kit for detecting MSAF that can be employed by unskilled users at home; d) Providing a platform for identifying etiologies for fetal distress after ROM has occurred; e) Providing an inexpensive home kit that will reduce medical costs by early identification of fetal distress; and (f) Providing a method and kit for differentiating between thick and thin MSAF.
An immunoassay system for home use by non-skilled personnel for detection of meconium in amniotic fluid is described in US20150346212A1 to the present inventor. However, it has been found that such an immunoassay system may be susceptible to damage during use. For example, the integrity of the seal may be breached or the transparency of the seal may be lost during use.
There is a need for an improved immunoassay system for detection of at least one analyte in a biological or non-biological fluid, which is suitable for use by unskilled personnel, which is reliable, durable and damage-resistant during storage and use.